1. Field of the Invention
The present invention relates generally to broadband amplifiers and communication systems, and more particularly to broadband booster amplifiers and communication systems with Raman and rare-earth doped amplifiers.
2. Description of Related Art
Because of the increase in data intensive applications, the demand for bandwidth in communications has been growing tremendously. In response, the installed capacity of telecommunication systems has been increasing by an order of magnitude every three to four years since the mid 1970s. Much of this capacity increase has been supplied by optical fibers that provide a four-order-of-magnitude bandwidth enhancement over twisted-pair copper wires.
To exploit the bandwidth of optical fibers optical amplifiers and wavelength-division multiplexing (WDM) have been developed and utilized in optical communications. Optical amplifiers boost the signal strength and compensate for inherent fiber loss and other splitting and insertion losses. WDM enables different wavelengths of light to carry different signals parallel over the same optical fiber. Although VDM is critical in that it allows utilization of a major fraction of the fiber bandwidth, it would not be cost-effective without optical amplifiers. In particular, a broadband optical amplifier that permits simultaneous amplification of many WDM channels is a key enabler for utilizing the full fiber bandwidth.
Silica-based optical fiber has its lowest loss window around 1550 nm with approximately 25 THz of bandwidth between 1430 and 1620 nm. In this wavelength region, erbium-doped fiber amplifiers (EDFAs) are widely used. However, the absorption band of a EDFA nearly overlaps its the emission band. For wavelengths shorter than about 1525 nm, erbium-atoms in typical glasses will absorb more than amplify. To broaden the gain spectra of EDFAs, various dopings have been added. Co-doping of the silica core with aluminum or phosphorus broadens the emission spectrum considerably. Nevertheless, the absorption peak for the various glasses is still around 1530 nm.
Broadening the bandwidth of EDFAs to accommodate a larger number of WDM channels has become a subject of intense research. A two-band architecture for an ultra-wideband EDFA has been developed with an optical bandwidth of 80 mn. To obtain a low noise figure and high output power, the two bands share a common first gain section and have distinct second gain sections. The 80nm bandwidth comes from one amplifier (so-called conventional band or C-band) from 1525.6 to 1562.5 nm and another amplifier (so-called long band or L-band) from 1569.4 to 1612.8 nm.
These recent developments illustrate several points in the search for broader bandwidth amplifiers for the low-loss window in optical fibers. First, even with EDFAs, bandwidth in excess of 40-50 nm requires the use of parallel combination of amplifiers. Second, the 80 nm bandwidth may be very close to the theoretical maximum. The short wavelength side at about 1525 nm is limited by the inherent absorption in erbium, and long wavelength side is limited bv bend-induced losses in standard fibers at above 1620 nm. Therefore, even with these recent advances, half of the bandwidth of the low-loss window, i.e., 1430-1530 nm, remains without an optical amplifier.
There is a need for a broadband amplifier and broadband communication system suitable for a wide range of wavelengths.
Accordingly, an object of the present invention is to provide a method of broadband amplification that divides an optical signal with a wavelength of 1430 nm to 1620 nm at a preselected wavelength into a first beam and a second beam.
Another object of the present invention is to provide a method of broadband communication that propagates a plurality of WDM wavelengths, with at least a portion of the WDM wavelengths in the range of 1430 to 1530 nm, from a trnsrmitter assembly along a transmission line.
Yet another object of the present invention is to provide a method of broadband communication that propagates a first plurality of WDM wavelengths in the wavelength range of 1530 to 1620 from a transmitter assembly along a transmission line, and introduces a second plurality of WDM wavelengths in the wavelength range of 1430 to 1530 to the transmission line.
In another embodiment of the present invention, a method of broadband amplification divides an optical signal of wavelength of 1430 nm to 1620 nm at a preselected wavelength into a first beam and a second beam. The first beam is directed to at least one optical amplifier and produces an amplified first beam. The second beam is directed to at least one rare earth doped fiber amplifier to produce an amplified second beam. The first and second amplified beams are combined.
In another embodiment of the present invention. a method transmitting WDM wavelengths in a broadband communication system includes propagating a plurality of WDM wavelengths from a transmitter assembly along a transmission line. At least a portion of the WDM wavelengths are in the wavelength range of 1430 to 1530 nm. At least a portion of the plurality of wavelengths are amplified with a Raman amplifier assembly to create a plurality of amplified WDM wavelengths. The plurality of amplified WDM wavelengths are received at a receiver assembly.
In another embodiment, a method of transmitting WDM wavelengths propagates a first plurality of WDM wavelengths in the wavelength range of 1530 to 1620 from a transmitter assembly along a transmission line. A second plurality of WDM wavelengths in the wavelength range of 1130 to 1530 is introduced to the transmission line; The second plurality of WDM wavelengths are amplified by Raman amplification after the second plurality of WDM wavelengths are introduced to the transmission line. The first and second pluralities of WDM wavelengths are received at a receiver assembly.
In another embodiment of the present invention, a method of transmitting WVDM wavelengths in a broadband communication system includes, propagating a plurality of WDM wavelengths from a transmitter assembly along a transmission line. At least a portion of the plurality of WDM wavelengths are in the wavelength range of 1430 to 1530 nm. A portion of the plurality of wavelengths are amplified with a Raman amplifier assembly to create a plurality of amplified WDM wavelengths that are received at a receiver assembly.
In another embodiment of the present invention. a method of transmitting WDM wavelengths in a broadband communication svstem includes propagating a first plurality of WDM wavelengths in the wavelength range of 1530 to 1620 from a transmitter assembly along a transmission line. A second plurality of WDM wavelengths in the wavelength range of 1430 to 1530 are introduced to the transmission line. The second plurality of WDM wavelengths are amplified by Raman amplification after the second plurality of WDM wavelengths are introduced to the transmission line. The first and second pluralities of WDM wavelengths are received at a receiver assembly.